Looking for the best moving coil cart that is around $5K used

I agree with tooblue.  Although the rewards might not come immediately, and it may require work on your part, I believe $5,000 is too much to spend on a cartridge, when your turntable seems to be a limiting factor(I have to admit to not being a fan of the one Scout[or Scoutmaster], although modified, I heard at a show.  It was not very dynamic, or emotion-inducing to me, but may have been limited due to the modifications.).

Papafrgog, I wouldn't worry so much about what others here say regarding your Linn.  First, I got to hear needledrops on PinkFish Media that, to me, showed me that a Linn Lp12 was the best of the bunch, which included an SME and the old Technics direct drive(with mods), among others.  The thing is, with music, it's not all an intellectual exercise.  In other words, you can get enjoyment from the actual music, unlike some other hobbies, where you worry if you really have the best.  Number 2:  I heard the Technics SP10 from a well-known audio company, and they also  do mods to this turntable.  It was not in the same league as a well set up Linn, at least by my standards, which includes enjoying the music, and getting off on it(maybe affecting you emotionally?).

I agree with mmakshak! A well-setup Sondek is indeed hard to beat! I have one myself, along with two Ariston RD's (the Linn's cousins). And I have kept them all in use, preferring them to today's pricier TT's! Get the best TT you can afford - even if it means skimping on the cartridge.

I don't want to write a treatise on analog v. digital. I have a Nantise/Lenco turntable with an Ikeda Kai cartridge, a 407 long tonearm, a Star Sound Platter Ground, and a H-Cat X12 current phono stage for analog.
  For digital I have a Surface touch screen control unit, and for digital, an AMS music server from Archiving Vinyl, an Avarii dac with JFET amplification. My digital sources are all double DSD initially on SACD.
  There are many differences. For one their sound stages differ. Digital is what the mikes receive and analog is what the recording engineer seeks and is more of what an audience hears. Second, there is more detail in digital, of instrument noises such as more harmonic as well as fingers sliding on strings. Finally, digital has highly defined locations of the sound stage and better high end.
  But analog is smoother, has more music hall or studio decay, and has more familiar instrument sounds with brass and drums not accurately reproduced.
  These observations come fro about ten instances where I have both analog and digital versions of recordings.
  There is no question that digital captures more detail and precise location of musicians and signers and that some of this is not music but it contributes to  realism.
  Vinyl, however, gives more hall decay and sounds familiar.

I read recently that the most important part of a phonograph system is the turntable, followed by the tonearm, folled lastly by the cart. It doesn't make any sense putting a $5K cart on a $400 TT/Arm. I would recommend selling your two tt setups and buying one new one of the best quality TT  and Arm possible and run it with the cart you have now.